The Sec20/Tip20p complex is involved in ER retrieval of dilysine-tagged proteins

Sec20p and Tip20p were previously identified as two interacting proteins involved in early steps of the secretory pathway in Saccharomyces cerevisiae. Here we describe a novel temperature-sensitive allele of TIP20 and analyze its phenotype. While sec20 and tip20 mutants exhibited a defect in forward ER-to-Golgi transport at the non-permissive temperature, both were also defective for retrieval of various dilysine-tagged proteins from the Golgi back to the endoplasmic reticulum (ER) at lower temperature. Dilysine-dependent Golgi localization of Emp47p was also defective in both mutants. These results suggest a role for the Sec20/Tip20p complex in retrieval of dilysine-tagged proteins back to the ER.